<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<div id="app">
  <span v-if="isShow">
    <label for="username">用户账号</label>
    <input type="text" id="username" placeholder="请输入你的账号..." key="username">
  </span>
  <span v-else>
    <label for="useremail">用户邮箱</label>
    <input type="text" id="useremail" placeholder="请输入你的邮箱..." key="useremail">
  </span>
  <button @click="isShow=!isShow">切换登录</button>
</div>


<script src="../js/vue.js"></script>
<script>
  const app = new Vue({
    el: '#app',
    data: {
      isShow: true
    }
  })
</script>
</body>
</html>